1. Field of the Invention
The invention relates to a protection system for aerial transmission lines.
2. Description of the Prior Art
Conventionally, aerial transmission lines for transmitting high voltage power are structured such that transmission lines of the respective phases are supported on arms of steel towers through suspension insulators. Recently, there is such a proposal that an arrester of zinc oxide constituted by a plurality of non-linear elements is inserted between each transmission line and a steel tower arm so as to make it possible to maintain a normal operation even in case of a thunder-bolt fault to supply power without interrupting service, as disclosed in the specification of Japanese Patent Unexamined Publication No. 86141/78.
Alternatively, arresters are used to cut off abnormal peak voltages in case of a thunder-bolt to thereby supply normal power.
Under the circumstances where stability and high reliability are required in supplying power, it becomes necessary to provide a transmission line protection system for supervising the state of contamination of the insulators or the like which are constituent components of the transmission lines and the occurrence of overvoltages in the transmission lines. Even if an overvoltage detecting means for apparatuses equipped on the ground in ordinary substations is intended to be applied as it is to a transmission line protection system, it is impossible to utilize such a means because the transmission lines are disposed at high positions, and in the case where the state of contamination or the overvoltage in the transmission lines is detected by such a means, a malfunction is caused due to a phenomenon of induction or the like, so that it is made difficult to perform highly reliable supervision of the transmission lines.